Spain is famous for its weather, Benidorm, Spanish food, it's football team, Barcelona, and basically being a rather sunny place overall â none of these descriptions are incorrect, and in fact they are all entirely true!
As the temperature of the air increases its density decreases. Therefore the thrust produced by the engine decreases. As the air pressure increases, its density increases, causing thrust produced by the engine to increase. Altitude has a double effect on thrust. As the altitude increases, the air becomes colder and denser, up to the beginning of stratosphere. This causes the thrust to increase.
As it sinks deeper into the atmosphere, the pressure from the weight of the air above it pushes air molecules closer together, causing them to become more agitated and heating them up again. As a result, their temperature rises, even though no heat has been added. This process is referred to as adiabatic warming.